U.S. patent application number 15/349690 was filed with the patent office on 2018-05-17 for adaptive vehicle braking systems, and methods of use and manufacture thereof.
The applicant listed for this patent is Honda Motor Co., Ltd.. Invention is credited to Yuichiro AKITA, Lorne R. DYAR.
Application Number | 20180134261 15/349690 |
Document ID | / |
Family ID | 62107175 |
Filed Date | 2018-05-17 |
United States Patent
Application |
20180134261 |
Kind Code |
A1 |
AKITA; Yuichiro ; et
al. |
May 17, 2018 |
ADAPTIVE VEHICLE BRAKING SYSTEMS, AND METHODS OF USE AND
MANUFACTURE THEREOF
Abstract
Some embodiments are directed to a controller is provided for
use with a vehicle braking system. The braking system can include
brake assemblies coupled to an actuator. The controller can be
configured to: receive data indicative of a requested braking
force; select a distance of travel and actuating force for the
actuator from respective predetermined ranges of values that are
based on a curve determined using discrete portions representing
constant incremental area under the curve for constant workload;
and signal the brake assemblies to output braking response based on
the selected distance of travel and actuating force of the
actuator.
Inventors: |
AKITA; Yuichiro; (Dublin,
OH) ; DYAR; Lorne R.; (Plain City, OH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Honda Motor Co., Ltd. |
Tokyo |
|
JP |
|
|
Family ID: |
62107175 |
Appl. No.: |
15/349690 |
Filed: |
November 11, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B60T 8/4081 20130101;
B60T 2270/406 20130101; B60T 7/042 20130101; B60T 2270/604
20130101; B60T 8/3255 20130101; B60T 2220/04 20130101; B60T 17/22
20130101; B60L 7/26 20130101; B60L 2250/26 20130101 |
International
Class: |
B60T 7/04 20060101
B60T007/04; B60L 7/26 20060101 B60L007/26 |
Claims
1. A controller for use with a vehicle braking system, the braking
system including brake assemblies coupled to an actuator, the
controller configured to: receive data indicative of a requested
braking force; select a distance of travel and actuating force for
the actuator from respective predetermined ranges of values that
are based on a curve determined using discrete portions
representing constant incremental area under the curve for constant
workload; and signal the brake assemblies to output braking
response based on the selected distance of travel and actuating
force of the actuator.
2. The controller of claim 1, wherein differing distance of travel
and actuating force ranges for which a constant workload curve is
to be applied are selectable for differing driving conditions.
3. The controller of claim 2, wherein differing distance of travel
and actuating force ranges for which a constant workload curve is
to be applied are selectable for high performance driving
conditions.
4. The controller of claim 2, wherein differing distance of travel
and actuating force ranges for which a constant workload curve is
to be applied are selectable for stop-and-go driving
conditions.
5. The controller of claim 2, wherein the selectable distance of
travel and actuating force ranges for each driving condition are
automatically adjustable to compensate for degradation in
performance of the brake assemblies.
6. The controller of claim 1, wherein the predetermined ranges of
values of distance of travel and actuating force for the actuator
are pedal stroke travel and pedal force of a brake pedal.
7. The controller of claim 1, wherein the predetermined ranges of
values of distance of travel and actuating force for the actuator
reflects previously collected data based on established leg-muscle
memory movement of vehicle operators.
8. The controller of claim 1, wherein the controller is further
configured to adjust the output braking response based on the
selected distance of travel and actuating force of the actuator
upon a determination of performance degradation of the brake
assemblies.
9. The controller of claim 1, wherein the curve on which the
predetermined ranges of values are based smoothly transitions
between the discrete portions each having a varied actuating force
to distance of travel ratio.
10. A braking system for a vehicle, comprising: at least one brake
assembly; an actuator configured to engage and disengage the at
least one brake assembly; and a controller in electronic
communication with the at least one brake assembly and the
actuator, the controller configured to: receive data indicative of
a requested braking force; select a distance of travel and
actuating force for the actuator from respective predetermined
ranges of values that are based on a curve determined using
discrete portions representing constant incremental area under the
curve for constant workload; and signal the at least one brake
assembly to output braking response based on the selected distance
of travel and actuating force of the actuator.
11. The braking system of claim 10, wherein differing distance of
travel and actuating force ranges for which a constant workload
curve is to be applied are selectable for differing driving
conditions.
12. The braking system of claim 11, wherein differing distance of
travel and actuating force ranges for which a constant workload
curve is to be applied are selectable for high performance driving
conditions.
13. The braking system of claim 11, wherein differing distance of
travel and actuating force ranges for which a constant workload
curve is to be applied are selectable for stop-and-go driving
conditions.
14. The braking system of claim 11, wherein the selectable distance
of travel and actuating force ranges for each driving condition are
automatically adjustable to compensate for degradation in
performance of the brake assemblies.
15. The braking system of claim 10, wherein the predetermined
ranges of values of distance of travel and actuating force for the
actuator are pedal stroke travel and pedal force of a brake
pedal.
16. The braking system of claim 10, wherein the predetermined
ranges of values of distance of travel and actuating force for the
actuator reflects previously collected data based on established
leg-muscle memory movement of vehicle operators.
17. The braking system of claim 10, wherein the controller is
further configured to adjust the output braking response based on
the selected distance of travel and actuating force of the actuator
upon a determination of performance degradation of the brake
assemblies.
18. The braking system of claim 10, wherein the curve on which the
predetermined ranges of values are based smoothly transitions
between the discrete portions each having a varied actuating force
to distance of travel ratio.
19. A method of calibrating a vehicle braking system that includes
brake assemblies coupled to an actuator, the method comprising:
receiving data indicative of a requested braking force; selecting a
distance of travel and actuating force for the actuator from
respective predetermined ranges of values that are based on a curve
determined using discrete portions representing constant
incremental area under the curve for constant workload; and
signaling the brake assemblies to output braking response based on
the selected distance of travel and actuating force of the
actuator.
20. The method of claim 19, the method further comprising adjusting
the output braking response based on the selected distance of
travel and actuating force of the actuator upon a determination of
performance degradation of the brake assemblies.
Description
BACKGROUND
[0001] The disclosed subject matter relates to adaptive vehicle
braking systems, and methods of use and manufacture thereof. More
particularly, the disclosed subject matter relates to methods and
apparatus that enhance vehicle operator feedback during
regenerative brake blending of hybrid vehicles.
[0002] Vehicle braking systems, particularly adaptive braking
systems, enhance hybrid vehicle performance by controlling
regenerative brake blending in which an electric motor functions as
a generator to slow the vehicle, in conjunction with traditional
braking systems. Electric actuation is used to achieve high
performance operation of vehicles having hybrid powertrains by
precisely controlling regenerative brake blending. These systems
can offer tailored pressure control maps to meet brake pedal
deceleration controllability.
SUMMARY
[0003] According to one aspect, a controller is provided for use
with a vehicle braking system, the braking system including brake
assemblies coupled to an actuator. The controller is configured to:
receive data indicative of a requested braking force; select a
distance of travel and actuating force for the actuator from
respective predetermined ranges of values that are based on a curve
determined using discrete portions representing constant
incremental area under the curve for constant workload; and signal
the brake assemblies to output braking response based on the
selected distance of travel and actuating force of the
actuator.
[0004] According to another aspect, a braking system for a vehicle
is provided. The braking system can include at least one brake
assembly. The braking system can also include an actuator
configured to engage and disengage the at least one brake assembly.
The braking system can further include a controller in electronic
communication with the at least one brake assembly and the
actuator. The controller is configured to: receive data indicative
of a requested braking force; select a distance of travel and
actuating force for the actuator from respective predetermined
ranges of values that are based on a curve determined using
discrete portions representing constant incremental area under the
curve for constant workload; and signal the at least one brake
assembly to output braking response based on the selected distance
of travel and actuating force of the actuator.
[0005] According to yet another aspect, a method can be provided
for calibrating a vehicle braking system that includes brake
assemblies coupled to an actuator, the method comprising: receiving
data indicative of a requested braking force; selecting a distance
of travel and actuating force for the actuator from respective
predetermined ranges of values that are based on a curve determined
using discrete portions representing constant incremental area
under the curve for constant workload; and signaling the brake
assemblies to output braking response based on the selected
distance of travel and actuating force of the actuator.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] The disclosed subject matter of the present application will
now be described in more detail with reference to exemplary
embodiments of the apparatus and method, given by way of example,
and with reference to the accompanying drawings, in which:
[0007] FIG. 1 is a schematic view of exemplary power and braking
systems for a vehicle in accordance with the disclosed subject
matter.
[0008] FIG. 2 is a detailed schematic view of the exemplary braking
system in accordance with the disclosed subject matter.
[0009] FIG. 3 is a schematic view of brake blending ratio control
in accordance with the disclosed subject matter.
[0010] FIG. 4 is a graph of pedal workload of the system in
accordance with the disclosed subject matter.
[0011] FIG. 5 is a graph of pedal stroke and pedal force in
accordance with the disclosed subject matter.
[0012] FIG. 6 is a graph of predictable brake pedal operation in
accordance with the disclosed subject matter.
[0013] FIG. 7 is a graph of unpredictable brake pedal operation in
accordance with the disclosed subject matter.
[0014] FIG. 8 is a flowchart of control logic of the braking system
in accordance with the disclosed subject matter.
[0015] FIG. 9 is a graph of brake fade consideration regarding
pedal stroke and force.
[0016] FIG. 10 is a graph of brake fade consideration regarding
slave cylinder stroke and system pressure.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0017] Overall, the disclosed embodiments of an adaptive vehicle
braking system focus on setting targets for human-centered high
performance, i.e., sports car driving that delivers a unique way to
further allow complete control of the vehicle dynamics with the
driver's exact intentions. Intuitive brake feeling is defined as
allowing the driver to easily find the intended deceleration
response without unintentional sacrifices. This concept is based on
human kinesthetic learning. Tactile learning can benefit drivers to
engage the brake controls to extract the exact desired
deceleration.
[0018] The brake pedal tuning system disclosed herein is for
electric or hybrid vehicles. Traditional automotive vehicles
typically utilize a brake pedal linked to a vacuum booster
actuation system to control deceleration by hydraulic pressure
control. Since the vacuum booster has limited tuning capability.
electric actuation can be used to customize the output pressure to
achieve a higher level of tuning capability.
[0019] The system therefore uses an electronic actuating mechanism
to achieve a predictable braking as experienced by the driver. To
accomplish this task, the brake pedal operation needs to be coupled
to human sensations. A progressive rate pedal stroke and pedal
force workload is established to enable a buildup sensation to
braking force lock point. A pedal stroke (i.e., pedal travel
distance) is mapped against pedal force range into the system
through previously collected data (e.g. drivers' leg movements). In
other words, the stroke and force modulation range is established
based on traditional leg muscle memory movement. Based on the
established ranges, the system will determine the travel/force
curve to apply during braking control as described below.
[0020] As the driver depresses the pedal, the pedal force felt by
the driver will increase in a progressive and predictable manner to
give the driver a "buildup sensation" through the pedal. As
discussed in more detail below, pedal force is increased by keeping
workload constant as the pedal is stroked (i.e., discrete segments
of curve providing a constant incremental area under the curve for
representing the same amount of workload as stroke minimizes and
force increases). This will provide the driver with intuitive pedal
feeling with predictive control.
[0021] The system could also be incorporated into an integrated
dynamic system (IDS) allowing for selection of different response
characteristics in differing driving settings (e.g., city, winding
road, track). In general, sports cars are driven on anything
ranging from urban streets to winding backroads and racetracks.
Each of these scenarios has ideal vehicle performance targets. The
brake feeling must be intuitive and consistent to allow harmonious
sensations with the scenario.
[0022] In the case of a city environment, the vehicle controls are
generally second nature and without much thought. The deceleration
must be easy to control without unexpected system output. In
addition, the pedal force must be appropriately set to prevent
tiresomeness under everyday stop-and-go workload.
[0023] In the case of the winding backroad environment, the driver
is more engaged with the vehicle dynamics. The driver demands
progressive and predicable control of the system as they enjoy the
vehicles handling performance. The systems' stroke/force
progressive buildup must be harmonious with the progressive setting
of the chassis. This smooth control compliments the effortless
transient movement.
[0024] In the case of the racetrack driving environment, the driver
is occupied with maximizing peak performance to achieve the lowest
lap time. This scenario demands ultimate control of threshold and
trail braking to maximize tire grip. In addition, minimal feeling
changes must occur with thermal changes under high energy driving
to enable brake consistency as the driver continues to lap the
track.
[0025] A few inventive aspects of the disclosed embodiments are
explained in detail below with reference to the various figures.
Exemplary embodiments are described to illustrate the disclosed
subject matter, not to limit its scope, which is defined by the
claims. Those of ordinary skill in the art will recognize a number
of equivalent variations of the various features provided in the
description that follows.
[0026] FIG. 1 is a schematic view of power and braking systems 20,
30 for a vehicle 10 in accordance with the disclosed subject
matter. The exemplary power system 20 of the present embodiment is
configured as a hybrid power unit including an engine, a
transmission, and an electric motor. Some embodiments may include
multiple electric motors such as two, three, four, five, etc. The
power system 20 is configured to communicate with the braking
system 30 by a communication line 22.
[0027] The exemplary braking system 30 includes brake assemblies 32
connected to a brake force control system 34 by brake lines 44,
where the brake force control system 34 includes a pedal 36 by
which a vehicle operator (i.e., driver) can operate the brake
assemblies 32. Each of the brake assemblies 32 includes a brake
disc 38, a caliper 40, and brake pads 42.
[0028] The disclosed braking system 30 achieves an intuitive brake
feeling in a variety of driving conditions, ultimate track
performance and reduction of CO2 emissions per vehicle. The system
30 integrates brake-by-wire with high-performance braking
hardware.
I. Overview
[0029] Advances in hybrid power train technology achieve ultimate
vehicle performance while reducing CO2 emissions. New powertrain
technologies enable instantaneous acceleration and torque vectoring
for direct yaw control to enhance vehicle dynamics and driver
enjoyment. Such systems also enable manufacturers to tailor vehicle
chassis response to varied driving scenarios by allowing the driver
to select settings ranging from electric (i.e., quiet mode) to
hybrid propulsion (i.e., track mode). The integration of these new
devices, developed with traditional sports car fundamentals,
enables the driver to experience consistent peak performance, new
levels of controllable line trace while cornering and reduced CO2
emissions through regenerative braking. To achieve high performance
with a hybrid power train, the braking system assists in powering
the chassis control devices. The braking system captures
regenerative braking energy to boost performance without
sacrificing vehicle dynamics control. In addition, the brakes
support the IDS to allow the driver to easily control the vehicle's
deceleration with the brake pedal.
[0030] Sports cars typically utilize a brake pedal linked to a
vacuum booster actuation system to control deceleration by
hydraulic pressure control. This system, connected to a
high-performance brake corner hardware system, generally offers
sports car brake deceleration controllability under at-limit
performance at the track. This single-priority tuning for one
chassis response sacrifices controllability in other areas.
Non-hybrid powertrains do not require regenerative braking control;
therefore, they do not require new actuation technology.
[0031] To maximize vehicle dynamic performance from a hybrid power
train, electric actuation must be used to precisely control
regenerative and friction brake blending. This system can support
the IDS by offering tailored pressure control maps to meet brake
pedal deceleration controllability to be intuitive and consistent
in all of the IDS settings. Intuitive brake pedal control means the
driver has a clear and predictable sense of deceleration based on
their braking intention. Consistency means the controllability and
repeatability is maintained in a wide range of driving scenarios,
from city streets to race tracks. In other words, the system can
support the IDS to faithfully translate the braking inputs of the
driver with incredible fidelity and virtually zero delay, thus
amplifying the capabilities of every driver, while greatly
elevating the dynamic experience in a wide range of driving
situations.
II. Brake Pedal Workload
[0032] Intuitive brake feeling occurs when the driver can easily
receive the intended deceleration response without unintentional
sacrifices to handling or performance. This concept is based on
kinesthetic, or tactile, learning, which is learning by performing
a physical activity. Intuitive braking enables drivers at all
levels, from novice to professional, to engage with the brake
controls and extract the desired deceleration. To accomplish an
intuitive braking feeling, brake pedal operation must be coupled
with human sensation.
[0033] FIG. 4 is a graph of pedal workload of the system in
accordance with the disclosed subject matter. As shown in FIG. 4, a
progressive rate of pedal stroke and pedal force workload, where
work is equal to the product of stroke distance and force on the
pedal, is established to enable a buildup sensation to the braking
force lock point.
[0034] The stroke and force modulation range was established based
on traditional leg muscle memory movement. The pedal operation
workload is constant, with smooth ratio changes that allow the
driver to maintain the same amount of workload, as the stroke
minimizes and the force increases, to establish the buildup
feeling.
[0035] FIG. 5 is a graph of pedal stroke and force in accordance
with the disclosed subject matter. The ratio R of the pedal stroke
S to the pedal force F transitions up to the lock point shown in
FIG. 4, with the area of the triangle equating to work. The curve
shown in FIG. 4 manages the ratio R such that the work is constant
throughout the braking progression. FIG. 6 is a graph of
predictable brake pedal operation, and FIG. 7 is a graph of
unpredictable brake pedal operation in accordance with the
disclosed subject matter. In FIG. 6, the work is constant with
smooth changes of the ratio R of pedal force F over pedal stroke S
across the triangular increments shown. FIG. 6 therefore represents
predictable and therefore intuitive characteristics of the pedal 36
of the braking system 30. Conversely, FIG. 7 shows ratio R changes
that are not smooth and therefore create a disjointed rather than
progressive braking progression, with inconsistent changes in pedal
stroke S and pedal force F approaching the lock point. FIG. 7
therefore represents unpredictable braking characteristics not
present in the disclosed braking system 30, and illustrates
differences from traditional braking systems. As shown in FIGS. 4
and 6, the constant workload (area under the curve) of the present
embodiment of the braking system 30 provides an intuitive pedal
operation modulation with the buildup sensation.
III. Multiple Driving Scenarios
[0036] In general, sports cars are driven on city streets, winding
roads and race tracks. Each of these scenarios has ideal vehicle
performance targets. The brake feeling must be intuitive and
consistent to allow a harmonious feeling with each scenario.
[0037] In the city scenario, vehicle controls are generally second
nature and mindless. Deceleration must be easy to control without
unexpected system output. Additionally, pedal force must be set
appropriately to prevent weariness in everyday stop-and-go
workloads.
[0038] In the winding road scenario, the driver is more engaged
with the vehicle dynamics. The driver demands progressive and
predictable control of the system while enjoying the vehicle
handling performance. The system's progressive buildup of stroke
and force must be harmonious with the progressive setting of the
chassis. This smooth control complements the effortless transient
movement.
[0039] In the track driving scenario, the driver is focused on
maximizing peak performance to achieve the shortest lap time. This
scenario demands ultimate control of threshold and trail braking to
maximize tire grip. Additionally, the thermal changes that occur
under high-energy driving must be minimally felt to enable braking
consistency as the driver continues their lap time attack, without
undue brake fade, for instance.
IV. System Hardware and Processes
[0040] Technology used in advanced braking systems can be broken
down into four areas: actuation system, corner hardware, system
cooling and system integration.
[0041] A. Actuation System
[0042] An electro-servo brake (ESB) system was facilitates
cooperative control of regenerative and hydraulic brakes.
Regenerative braking is required to charge the hybrid powertrain
for electric motor propulsion, torque vectoring and reduced fuel
consumption from an internal combustion engine. The present
embodiment of the braking system 30 yields ESB smooth blending
between regenerated electric energy and hydraulic pressure in
braking functions.
[0043] In conventional brake systems, there is a fixed relationship
between brake line pressure and pedal stroke. The ESB system
achieves variable servo ratio control applied by conventional brake
pedal operation, as shown in detail in FIG. 2 and described below.
Therefore, in a conventional system, IDS brake feel cannot be
achieved because high-accuracy brake control only applies to one
setting.
[0044] 1. Hardware
[0045] FIG. 2 is a detailed schematic view of the exemplary braking
system 30 in accordance with the disclosed subject matter. The
system 30 in FIG. 2 includes a master cylinder assembly 50 and a
slave cylinder assembly 70 coupled to the brake assemblies 32. A
processor (ECU) 46 in communication with an electric motor and
regenerative braking controller 48 controls operation of the
braking system 30. As will be described below, the processor 46 can
include a drive mode select switch 47 to enable a vehicle operator
to switch between various driving modes suited to various scenarios
such as city and track driving.
[0046] The master cylinder assembly 50 includes the pedal 36
connected to a first piston 52, a first spring 54, a second piston
56 and a second spring 58. A pedal sensor 37 is in communication
with the pedal 36 to sense stroke distance. A chamber surrounding
the aforementioned pistons and springs is connected to a first
reservoir 60 having a cap 62. The master cylinder assembly 50
facilitates pressurization of hydraulic fluid in the brake lines 44
to actuate the brake assemblies 32 as a result of the pedal 36
being depressed. Specifically, the brake assemblies 32 are
controlled by a brake modulator 63 to effectively distribute
hydraulic pressure thereto.
[0047] The brake lines 44 by which the master cylinder assembly 50
is connected to the brake modulator 63 can be opened or closed via
first and second valves 92, 94 depending on whether or not
regenerative braking is activated, as described in more detail
below. Valve springs 95 bias the first and second valves 92, 94
open and the third valve 96 closed under normal operation. When
regenerative braking is deactivated, the first and second vales 92,
94 are open and depressing the pedal 36 serves to actuate the brake
assemblies 32. However, when regenerative braking is activated, the
first and second vales 92, 94 can be partially or fully closed to
disconnect the master cylinder assembly 50 from the brake modulator
63. As will be described below, regenerative braking instead
utilizes the slave cylinder assembly 70 to actuate the brake
assemblies 32 via the brake modulator 63. In order to continue to
provide braking feedback to the vehicle operator, a simulator 64
including a third piston 66 and a third spring 68 is connected to
the master cylinder assembly 50. In this setup, depressing the
pedal 36 pressurizes the brake lines 44 ahead of the first and
second valves 92, 94, which thereby acts on the internals of the
simulator 64 to provide feedback from the hydraulic pressure to the
vehicle operator. The brake line 44 connecting the simulator 64 to
the master cylinder assembly 50 also includes a third valve 96 that
opens and closes opposite the first and second valves 92, 94. Each
of the valves is also in communication with the processor 46 to
communicate pressure in the brake lines 44, and a first pressure
sensor 98 is disposed at the first valve 92 on connected brake line
44 to determine system pressure ahead of the first and second
valves 92, 94 when they are closed.
[0048] The slave cylinder assembly 70 includes a slave motor 72
connected to a ball screw 76 by a driveshaft 74, the screw 76 being
coupled with a fourth piston 78 and fourth spring 79, and fifth
piston 80 and fifth spring 81. A chamber surrounding the
aforementioned pistons and springs is connected to a second
reservoir 82 connected to the first reservoir 62 by the brake line
44. The slave cylinder assembly 70 facilitates pressurization of
hydraulic fluid in the brake lines 44 to actuate the brake
assemblies 32 as a result of the slave motor 72 being actuated by
the processor 46. Specifically, the brake assemblies 32 are
controlled by a brake modulator 63 to effectively distribute
hydraulic pressure thereto. As shown in FIG. 3 and described below,
the slave cylinder assembly 70 is configured to deliver the
appropriate braking pressure to the brake modulator 63 given a
position of the pedal 36, regardless of whether regenerative
braking has been activated. The processor 46 receives intended
system pressure from the first pressure sensor 98, and then
administers corresponding pressure via the slave cylinder assembly
70, which can then be monitored by the second pressure sensor
99.
[0049] This ESB system adopts new pressure control logic to
accomplish precise pedal feel at high pedal input. It calculates
target pressure demand based on the master cylinder pressure
signal. FIG. 3 is a schematic view of brake blending ratio control
in accordance with the disclosed subject matter. As shown in FIG.
3, the brake pedal stroke, vehicle speed, and master cylinder
assembly system pressure are all input to the processor to
calculate target brake pressure control, which selects which
braking map to apply. That information, along with an upper-limit
regenerative braking force the motor is able to provide, are
analyzed by the processor to determine brake distribution control.
Brake distribution control analyzes whether the target brake
pressure control can be achieved with just regenerative braking, or
if hydraulic braking needs to supplement the regenerative braking
to achieve the target brake pressure given the operator input via
the pedal. Ultimately, the processor proceeds from brake
distribution control to instruct the slave motor and/or the
regenerative braking motor/generator to match the braking input
from the pedal.
[0050] Other electric servo brake systems use the pedal stroke
signal only to calculate target pressure based on driver demand.
That generates higher levels of hysteresis when high deceleration
and pedal forces are required due to resolution limitations. These
limitations obstruct the driver's ability to precisely control
pedal modulation.
[0051] 2. Control Logic
[0052] FIG. 8 is a flowchart of control logic of the braking system
in accordance with the disclosed subject matter. The control logic
100 for the processor shown in FIG. 8 is initiated by pedal
modulation at step S110, in the form of operator/driver braking
input on the pedal with the intent to engage the vehicle
brakes.
[0053] Once the driver has shown intent to use the braking system
by modulating the pedal, the IDS mode is determined at step S120.
The IDS mode may be set to city driving, track driving, etc., each
of which have unique driving characteristics desired. The logic
then proceeds to check whether or not track mode, or an equivalent
race-inspired high performance mode, is selected as the IDS mode at
step S130. If it is determined that track mode has not been
selected, the logic proceeds to select a normal map at step S160.
Once a normal map has been selected, the pedal stroke S is
determined from the pedal sensor at step S190. Given the pedal
stroke S, the braking map is shifted to compensate for potential
performance degradation at step S200.
[0054] After the above described steps have been initiated, the
logic then determines whether or not the brakes are still being
applied at step S210. If the brakes are no longer being applied,
the logic ends at step S220. If the brakes are indeed still being
applied, the logic proceeds back to step S130 to determine whether
or not track mode is selected.
[0055] If at step S130 it is determined that track mode is
selected, the logic proceeds to select the track map for the
braking system performance at step S140, as the track map for the
braking system may be only one of several different system maps
configured to be included within track mode. Having selected the
track map for the braking system at step S140, the logic proceeds
to detect brake pressure Pin the system ahead of the valves and the
system stroke change of the slave cylinder at step 150. Having
detected system pressure P and stroke change of the slave cylinder,
the logic determines whether or not those metrics indicate a fade
condition of the brake assemblies at step S170. If a fade condition
is not indicated, the logic proceeds to step S190 to determine the
pedal stroke from the pedal sensor at step S190. At this point, the
logic follows the above described path to step S200 and subsequent
steps.
[0056] If at step S170 a fade condition is detected, the logic
proceeds to step S180 at which the braking system shifts the track
map. The track map parameters can be shifted as shown in FIGS. 9
and 10 to accommodate the detected fade and thereby ensure the
braking system maintains intuitive brake feeling for the vehicle
operator. Specifically, the system can artificially apply more
braking force to the degraded braking system given the same
operator input in the form of pedal stroke and force.
[0057] This control logic ensures that despite wear and tear of
vehicle operation, the vehicle and braking system continue to offer
the intuitive feedback and buildup sensation to the driver to
enhance operability of the vehicle.
[0058] B. Brake Assembly Hardware
[0059] Lightweight components can be used to further control total
system weight. This braking system can apply carbon ceramic matrix
(CCM) brake disk material due to its low density and light weight,
low displacement fixed aluminum calipers. The combination of these
components offers a reduction in unsprung mass over other vehicle
braking systems. Friction material selection is based on its
balance with the following established controllability priorities:
mu variation based on thermal effects, mu variation due to speed
sensitivity and minimum wear characteristics based on continuous
lapping.
[0060] C. System Cooling
[0061] Disk and caliper sizing are optimized based on the cooling
performance of the exemplary vehicle layout. The brake cooling
layout is integrated into the overall flow balance to optimize
aerodynamic drag, vehicle lift, down force and brake cooling. The
brake system cooling focus was to ensure brake pad temperatures
stabilized during at-limit lapping. This was accomplished by
optimizing the air flow to the front and rear brake calipers and
disks. The target brake pressure control and brake distribution
control, as discussed above and shown in FIG. 3, assist the braking
system in maintaining operable brake pad temperatures that do not
negatively affect vehicle performance.
[0062] D. System Integration
[0063] The electro-servo brake system is a brake-by-wire system
that needs to integrate the demands of a sports car system. The
corner hardware and cooling system manages the heat, but the
actuation system must actively control the pressure maps based on
the fluid consumption demand in each driving scenario.
[0064] One example of this integration is the consideration of
pressure control map changes based on effectiveness to achieve
intuitive brake pedal feel in a wide range of conditions. Friction
material generally offers different levels of performance at
different temperatures. To enable clear driver control, another
pressure map is included to compensate for track (circuit) driving,
enabling the driver to maintain the controllability feeling that
was experienced at city or winding road driving.
[0065] For example, the IDS adapted to public road driving may have
the following braking system characteristics: ambient
(approximately 100 degrees Celsius) brake pad temperature, low
brake pad coefficient of friction, low caliper fluid consumption,
with the ESB calibrated for the best setting for intuitive feeling.
Another example has the IDS adapted to track driving, which may
have the following braking system characteristics: brake pad
temperature between approximately 300 and 500 degrees Celsius, high
brake pad coefficient of friction, high caliper fluid consumption,
and again with the ESB calibrated for the best setting for
intuitive feeling.
[0066] Another example of this integration is the consideration of
brake fade. All systems can experience brake fade due to
degradation or poor maintenance of the system. Moving large
quantities of air across the friction brakes means that drivers
experience very little fade when braking during high-performance
and track driving. However, stroke change control logic was
developed to provide similar brake fade information to the
driver.
[0067] FIGS. 9 and 10 are graphs of brake fade considerations
regarding pedal stroke and force, and slave cylinder stroke and
system pressure. FIG. 9 shows an exemplary control logic/map change
to counteract effects of brake fade in an effort to maintain
intuitive brake pedal operation by the driver. FIG. 10 shows an
exemplary control logic/map change to similarly counteract effects
of brake fade, however in this case slave cylinder operation is
adjusted rather than the pedal stroke and force required. Depending
on whether or not regenerative braking has been activated, the
graphs in FIGS. 9 and 10 are representative of the map changes
required to maintain intuitive braking system feel. Furthermore, a
visual or auditory message may be presented to the vehicle operator
indicating brake fade and the system compensation discussed above.
The ability of the system to change control logic/maps during
instances of brake fade assists the system in achieving intuitive
and consistent brake deceleration controllability in all
scenarios.
[0068] A progressive rate pedal stroke and pedal force workload was
established to enable a buildup sensation to the braking force lock
point. The ESB system enables precise pressure map tuning to enable
constant workload with smooth ratio changes, allowing the driver to
maintain the same amount of workload, as the stroke minimizes and
the force increases, to establish the buildup feeling. This
provides an intuitive pedal feeling with predictable control.
Consistent intuitive brake deceleration is achieved though hardware
integration and changing ESB pressure maps during track driving.
The cooling system manages brake pad and fluid temperatures to
stabilize friction coefficient performance under at-limit track
lapping. The ESB pressure map is configured to be adjusted based on
high-temperature friction coefficient and fluid consumption
characteristics to achieve similar feeling as the public road
setting. Finally, the use of regenerative brake energy to drive the
motor reduces the workload on the engine, contributing to increased
fuel economy and reduced CO2 emissions.
V. Alternative Embodiments
[0069] While certain embodiments of the invention are described
above, and FIGS. 1-10 disclose the best mode for practicing the
various inventive aspects, it should be understood that the
invention can be embodied and configured in many different ways
without departing from the spirit and scope of the invention.
[0070] For example, embodiments are disclosed above in the context
of the adaptive vehicle braking system 30 configured for use with
regenerative braking of the hybrid vehicle 10 as shown in FIGS. 1
and 2. However, embodiments are intended to include or otherwise
cover adaptive braking systems integrated in other vehicles having
varied drivetrains and propulsion methods, such as pure
electric.
[0071] While the subject matter has been described in detail with
reference to exemplary embodiments thereof, it will be apparent to
one skilled in the art that various changes can be made, and
equivalents employed, without departing from the scope of the
invention. All related art references discussed in the above
Background section are hereby incorporated by reference in their
entirety.
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